The combination of nanoscale structures with biomolecules opens the door to novel biology and nanotechnology applications [1-6]. Controls over the material structure at the nanoscale are revolutionizing a wide range of fields and applications. This leads to improved characteristics and functions, as well as significant enhancement of optical, mechanical, electrical, structural, and magnetic properties of nanomaterials. Nanoparticles have been employed for a number of applications such as enzyme immobilization and drug delivery systems to solve various health problems. Nanomaterials are expected to have further impact on biomedicine, biosensors, diagnostics, and drug delivery systems [7-9].
Carbon nanotubes (CNTs) and their compatibility with aqueous environments have made it possible to interact with biological components including mammalian cells. Chemical functionalization of CNT surface, allows the functionalized CNT molecules (f-CNT) to be explored in advanced biotechnological applications. Functionalization is one of the most commonly used strategies to make CNT soluble in aqueous media. It makes f-CNT useful for biomedical applications. Carbon nanotubes can be functionalized either by covalent or noncovalent methodologies. Various biological applications of functionalized carbon nanotubes (f-CNTs) include their use as substrates for neuronal cell growth, as bioseparators and biocatalysts [10-14].
Recently, carbon nanotube-based field-effective-transistors (FET) have been developed which are used for DNA-based biomolecular recognition. Carbon nanotubes attached with single-strand DNA chains (ssDNAs) are used as probes for detecting their complementary DNA molecules specifically grafted over the FET substrate. The hybridization is detected by using redox method [15-18]. Carbon nanotubes can be used as stores for DNA or peptide molecules which have high potential in gene delivery system and molecular therapy of diseases [19-20].
Carbon nanotubes can also be used to fabricate nanomotors, which can enter inside the cells to treat diseases. So far, the influence of carbon nanotubes and the associated nanomaterials or nanodevices on human health and environment has been a focus of current investigation. Carbon nanotubes can be functionalized to achieve improved properties and functions such as biocompatibility and biomolecular recognition capabilities [21-22]. The potential with which carbon nanotubes can be applied in biomedical engineering and medicinal chemistry is highly dependent upon their biocompatibility. Carbon nanotubes exhibit cytotoxicity to human keratinocyte cells [23-24], can inhibit the growth of embryonic rat-brain neuron cells [25] and induce the formation of mouse-lung granulomas [26-28]. Computational model has shown that CNT fits snugly into the major groove of double standard DNA, since the diameter of single-walled CNT is compatible with the size of the DNA major groove. Moreover, CNT is a semi conducting material which offers the possibility of being used as switching device. The geometry of the combined DNA and CNT system was modeled using the CHARMM computational package with a properly adapted graphitic carbon force field for treating CNTs. Hybridization of electronic orbital between the CNT and the DNA is also included in this model [29-31]. In another approach, streptavidin-functionalized SWCNT was directed to the right location on the scaffold dsDNA molecule. SWNTs were solubilized in water by micellization in SDS. The solubilized SWNTs were functionalized with streptavidin by nonspecific adsorption [32-33]. Fluorescence microscopy of SWNTs with fluorescently labeled streptavidin indicated homogeneous coverage of the nanotubes with streptavidin [34].
Carbon nanotubes have several advantages for drug delivery: i) size in the range of 10-40 nm, ii) ability to provide a rod-like scaffold, iii) increased capacity to carry drugs, iv) ability to deliver drugs to the nucleus and v) inert and non-toxic nature. Researchers have obtained evidence showing the potential of carbon nanotubes in directed and targeted delivery of peptides and nucleic acids [35-36]. Moreover modification of nanotubes by adding certain functional groups enabled delivery of small peptides into the nuclei of fibroblast cells [37]. Although the mechanism of how tubes enter and leave cells is unclear, they appear to be non-toxic.
Chitosan has been shown to deliver genes into cells, but delivery of peptides by chitosan is limited. We reasoned that CNT coated with chitosan may facilitate peptide delivery and chitosan may reduce the toxicity of CNT to cells.